Chronograph
A chronograph is a watch with a built-in stopwatch function operated via pushers, with elapsed time read off subdials.
A chronograph is a watch that includes a stopwatch function in addition to telling the time. Pushers on the case (typically two — one at 2 o'clock for start/stop, one at 4 o'clock for reset) trigger a separate gear train that drives an elapsed-seconds hand on the central pinion and elapsed-minutes (and sometimes hours) on subdials.
Chronographs are commonly used for timing intervals — diver decompression stops, lap times at the track, pulse counting via a "pulsometer" or "tachymeter" scale on the bezel. The chronograph mechanism is one of the more complex standard complications and historically commands a premium over a comparable three-hand watch.
Notable chronograph movements include the Valjoux 7750 (the workhorse Swiss automatic chronograph movement, used by everyone from Tudor and Sinn to Hamilton and Oris), the Seiko 8R48/6S37, the Lemania 5100 (long discontinued but legendary among collectors), and high-end in-house movements like the Omega Caliber 9900, Rolex 4130, and the column-wheel chronographs from Patek, Vacheron, and Lange.
Famous chronograph watches include the Omega Speedmaster ("Moonwatch"), Rolex Daytona, Heuer Monaco, Breitling Navitimer, and Tudor Black Bay Chrono.
Common questions
Are chronograph and stopwatch the same thing?
Effectively yes. A chronograph is a watch with a built-in stopwatch — the central seconds hand normally sits at 12 and only moves when the user starts the timer via the pushers.
Can you use a chronograph as a regular seconds hand?
Most chronographs have a separate small running seconds subdial for the time itself, with the central seconds hand reserved for the stopwatch function. Leaving the chronograph running constantly accelerates wear on the movement and is generally discouraged.